This invention relates to a solid battery and a method for manufacturing an electrode of a solid battery. The electrode is useful as a positive electrode or a negative electrode of a fully solid type lithium ion battery.
As electronic devices such as mobile phones tend to be made compact and have upgraded functions, requirements for a battery which is a power source in such devices tend to become upgraded. Particularly, development has been made for providing a lithium ion battery having a high energy density.
An electrolyte which is made by impregnating a porous film called a separator with a non-aqueous electrolyte has been generally used as an electrolyte in a lithium ion secondary battery. Recently, instead of such electrolyte using mainly liquid, a lithium ion secondary battery (polymer battery) using a polymer electrolyte made of a polymer has been developed.
Further, as disclosed in Japanese Patent Application Laid-open Publications Hei 6-140052 and 2004-348972, there have been reports about assembly of a lithium ion secondary battery by using a solid electrolyte which is added with an inorganic oxide such as alumina in an electrolyte to improve mechanical strength and by using a fully solid electrolyte which is made by pressing a solid inorganic substance such as sulfide glass to pellets. Since these solid electrolytes do not use a combustible organic solvent such as an electrolytic solution, there is no danger of leakage or combustion and therefore these solid electrolytes are excellent from the standpoint of safety.
In the case of such a fully solid battery, all of a positive electrode, an electrolyte and a negative electrode are solid. As shown schematically in FIG. 4, in such fully solid battery 1, a positive electrode 2 and a negative electrode 3 are stacked together via a solid electrolyte 4 constituting a separator, and a positive electrode current collector 5 is provided on the outer surface of the positive electrode 2 and a negative electrode current collector 6 is provided on the outer surface of the negative electrode 3. These electrodes 2 and 3 are made, for example, by mixing powdery active materials 2a and 3a of the electrode with powdery electrolytes 2b and 3b to form a slurry, forming this slurry to a film and drying and sintering the film.
Such electrode 2 has a disorderly structure in which the active material 2a of the electrode and the electrolyte 2b of the electrode are mixed randomly and, since there is no orderly path for ion in the electrode 2, ion must pass through a long, disorderly path with the result that it takes a long period of time for a battery reaction and therefore it is difficult to provide a battery having a high current output. Further, since distance of diffusion of ion and electron in the active material 2a of the electrode is long, it is difficult to obtain a high current density.
It is, therefore, an object of the invention to provide a solid battery having a high current output and providing a high current density by improving an arrangement of the active material of the electrode and the electrolyte of the electrode which constitute the electrode.
It is also an object of the invention to provide a method for manufacturing an electrode of such improved battery.